Researchers find solar flares can cause GPS receivers to fail

Researchers find solar flares can cause GPS receivers to fail

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USA, 26 September 2006: Strong solar flares cause GPS receivers to fail, Cornell University researchers have discovered. Because solar flares – larger-than-normal radiation “burps” by the sun — are generally unpredictable, such failures could be devastating for “safety-of-life” GPS operations — such as navigating passenger jets, stabilizing floating oil rigs and locating mobile phone distress calls.

“If you’re driving to the beach using your car’s navigation system, you’ll be OK. If you’re on a commercial airplane in zero visibility weather, maybe not,” said Paul Kintner Jr., Professor of Electrical and Computer Engineering at Cornell and Head of Cornell’s GPS Laboratory.

Alessandro Cerruti, a graduate student working for Kintner, accidentally discovered the effect on Sept. 7, 2005, while operating a GPS receiver at Arecibo Observatory in Puerto Rico, one of six Cornell Scintillation Monitor (SCINTMON) receivers. Cerruti was investigating irregularities in the plasma of the Earth’s ionosphere — a phenomenon unrelated to solar flares — when the flare occurred, causing the receiver’s signal to drop significantly.

To be sure of the effect, Cerruti obtained data from other receivers operated by the Federal Aviation Administration (FAA) and the Brazilian Air Force. It was found that all the receivers had suffered exactly the same degradation at the exact time of the flare regardless of the manufacturer. Furthermore, all receivers on the sunlit side of the Earth had been affected.

The team was initially confused as to why the flare had caused the signal loss. Then Kintner recalled that solar flares are accompanied by solar radio bursts. Because the bursts occur over the same frequency bands at which GPS satellites transmit, receivers can become confused, leading to a loss of signal.

Had the solar flare occurred at night in Puerto Rico or had Cerruti been operating SCINTMON only at night, he would not have made the discovery.

“We normally do observations only in the tropics and only at night because that’s where and when the most intense ionospheric irregularities occur,” said Kintner. However, since no one had done it before, Cerruti was looking at “mid-latitudes” (between the tropics and the poles), where weaker irregularities can occur both night and day. As a result, SCINTMON detected the solar flare.

The full results of the discovery will be published in a forthcoming issue of the journal Space Weather.

– About Global Positioning System Laboratory (GPSL) at Cornell University
The Global Positioning System Laboratory (GPSL) at Cornell University investigates Global Navigation Satellite Signals for the purpose of remote sensing of the space environment, to improve the reliability and integrity of GPS positioning in the presence of space weather, and to advance GPS receiver technology.

GPSL is an interdisciplinary group composed of faculty, students, and staff who design and build GPS receivers, evaluate and test these receivers in both terrestrial and space environments, and teach courses in the design of GPS receivers. The GPSL has an international reputation for evaluating space weather effects on GNSS signals and positioning accuracy, acquisition of weak GNSS signals, and the development of GPS software receivers.